A video chip typically comprises a matrix of pixels consisting of a storage capacitor and a pass transistor. Data stored in the various capacitors collectively comprise a video image. The stored image is "read" out by shining a light on the chip and visually scanning the image.
This mode of outputting the stored contents poses a problem in the manufacture of such chips. Testing a video chip is not possible until the chip is packaged so that it is functional as an imaging device. This permits a test image to be loaded into the device and then visually inspected for defects. Defective devices can then be identified, removed from the lot and discarded. Thus, a defect is not detected until the chip is fully packaged. This is a costly process because the manufacturing cost has already been invested in producing the packaged part, which has now been determined to be defective.
It is therefore desirable to have the capability of screening out defective video chips prior to their being packaged in a final form. What is needed is a scheme for providing a suite of tests to the chip to fully verify the operability of the device before final packaging of the device.